Nowadays we are witnessing ever more significant integration of non-metallic materials (composites, plastics, etc.) in certain structures, structures of aircraft elements for example. The object of employing such materials is to reduce the weight of such structures as well as their cost of fabrication with respect to similar structures made of metal.
However, this substitution of materials gives rise to problems linked with the low electrical conductivity of the composite materials used, or even with their absence of conductivity.
Accordingly, such materials do not make it possible to ensure sufficient electrical conductivity making it possible to produce electrical links ensuring functions such as the return of current in an aircraft. To alleviate this functional deficiency, one is generally constrained to provide for the installation, on the surface of the composite structure considered, of conductors as well as of elements ensuring the fixing of these conductors to the structure and the interconnection of these conductors with those carried by neighboring structures.
However, such a solution penalizes the equipment in which the structure is integrated, as much in terms of weight as in terms of bulkiness or production time. These drawbacks take on particular significance when dealing with aircraft structures.
Furthermore, assembling a standard electrically conducting element, such as a monolithic conductor like a metallic wire or a strip, or else such as a conductor formed of a one-dimensional arrangement of conductors such as for example a multistrand electrical cable, with a structure made of composite material, may furthermore bring about mechanical stresses imposed on the conducting element. These stresses are due in particular to the differential expansions which occur at the level of the materials constituting the various assembled elements when the structure is subjected to significant temperature variations. Such is for example the case for civil aircraft structures which are subjected to temperatures that may range from −45° C. to +70° C., or else for space launcher structures which are subjected to temperatures that may range from −60° C. to +200° C. They are also due, to a lesser extent, to the installing of conductors on structures not necessarily having plane shapes.
Moreover, this substitution of materials also gives rise to problems linked with the integrity checking of the structures considered. Indeed, when a composite material structure undergoes a “low-energy” impact, due to the dropping of a tool, for example, the internal damage caused by the shock may appreciably reduce the mechanical performance of the structure, even though the detection of this damage by simple visual inspection is almost impossible, in contradistinction to the case of a metal structure.
However, there does not exist to date any known solution making it possible to directly integrate current-conducting elements with a composite structure while limiting the mechanical stresses imposed on said conductors, which stresses are generated by the shrinking or the stretching of the composite structure when it is thermally loaded and making it possible at the same time to note by simple visual inspection the possible presence of an impact zone on the surface of the structure.
Moreover, the impact resistance of composite material structural elements is taken into account by design offices, but leads to an overdimensioning of the structure with respect to the simple need for mechanical strength. This overdimensioning, the aim of which is to strengthen the resistance of these structural elements to an impact, does not allow definitive visual detection of a low-energy impact that may have damaged the structural element concerned.
The present concept is aimed at alleviating these drawbacks.